The pink river dolphin is the largest of the river dolphins and lives in the freshwater of the Amazon River. This species looks like the grey dolphin, but individuals are bigger, and, instead of a dorsal fin, they have a hump on their back. Their tails are also bigger. The brain of the river dolphin is 40% larger than a human brain. The pink dolphin has been listed as endangered due to pollution, overfishing, excessive boat trafficking, and habitat loss.